Medical dressing having a thermally expandable passage

Abstract

A bilayer laminated medical dressing having a thermally expandable passage is provided. The medical dressing achieves gas permeability as a function of temperature by cutting a star-shaped hole through the dressing when the dressing is flat and relaxed. On warming, the leaves between the radial cuts of the star-shaped hole curl and increase the hole size. Such a material is useful as a medical dressing.

We claim: 
     
       1. A flexible medical dressing asymmetrically laminated from at least two plastic layers disposed adjacent to each other and having different coefficients of thermal expansion, the medical dressing having a non-straight slit, wherein the slit forms a passage through the plastic layers, which passage varies in size with temperature, at least over a certain temperature range, at a rate greater than the thermal coefficients of expansion of the plastic layers. 
     
     
       2. A flexible medical dressing according to claim 1, wherein the slit has a form of a plurality of slots radiating from a junction. 
     
     
       3. A flexible medical dressing according to claim 2, wherein the junction is an aperture. 
     
     
       4. A flexible medical dressing according to claim 2, wherein an angle between at least one pair of adjacent slots is at most 90°. 
     
     
       5. A flexible medical dressing according to claim 1, wherein the layers of the medical dressing are dimensionally inert to moisture.